feat(auth): add WorkOS and Keycloak SSO providers (rebased) (#220)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/auth/sso.controller.ts

@@ -0,0 +1,10 @@
+import { Controller, Get } from '@nestjs/common';
+import { buildSsoDiscovery, type SsoProviderDiscovery } from '@mosaic/auth';
+
+@Controller('api/sso/providers')
+export class SsoController {
+  @Get()
+  list(): SsoProviderDiscovery[] {
+    return buildSsoDiscovery();
+  }
+}